The invention relates to a method of measuring the intensity of a DC current, particularly a high current; it also relates to a device implementing this method.
An electric current is traditionally measured by using a shunt, that is to say a device based on Ohm's law. Consequently, in order to be measurable, the voltage drop across the shunt must be significant and this voltage drop is also directly related to the dissipation by Joule effect of the shunt itself. Since any resistive material is related to a temperature coefficient, the temperature variations of the shunt cause systematic errors in measuring the current. This problem is particularly important for measuring high currents where the shunts are bulky and expensive sub assemblies. The purpose of the invention is to overcome this type of problem.
For this, the invention provides a method for measuring the intensity of a DC current flowing in the circuit, in which method said current is caused to flow in a magnetic coil for creating a magnetic field in a given volume of space, in determining at least the temperature of said coiled magnet and measuring the value of the magnetic field in said given volume, this value being representative of the strength of the current, knowing said temperature.
So as to have a more direct measurement of the strength of the current, the temperature of the magnetic coil may be stabilized by simple means. Furthermore, the magnetic field will be measured preferably by using the nuclear magnetic resonance phenomenon on a sample of chosen atoms, placed in a zone where the above mentioned magnetic field has a field sufficient homogeneity for using said phenomenon.
The invention also relates to a device for measuring the strength of a DC current flowing in a circuit, including a magnetic coil intended to be inserted in series in said circuit for generating a magnetic field in at least a given volume of space, means for determining at least the temperature of said magnet and means for measuring the magnetic field in said given volume.
Means will preferably be provided for stabilizing the temperature of the magnet, for example a control line regulating the temperature of a fluid cooling said magnet. As mentioned above, the magnetic coil will be preferably formed so that the magnetic field is sufficiently homogeneous in said given volume for allowing a nuclear magnetic resonance phenomenon to be used, and an NMR probe, known per se, will be placed in said given volume for measuring the value of the magnetic field.